The present invention relates to a rotary actuator which is operable under the influence of fluid pressure to rotate a drive member.
A known rotary actuator includes two internal and two external splines. Thus, the known actuator assembly includes a drive member upon which external helical splines are formed. Internal splines on a piston sleeve engage the splines on the drive member. External splines on the piston sleeve are engaged by a stationary ring gear. Fluid pressure causes the piston sleeve to move axially in a motor cylinder chamber.
As the piston sleeve of this known rotary actuator moves in the chamber, the external helical spline on the drive member and the internal helical spline on the piston sleeve cause the drive member to rotate. In addition, the interaction between the helical spline on the outside of the piston sleeve and the stationary ring gear causes the piston sleeve to rotate. This rotational movement of the piston sleeve is transmitted to the drive member. Since the piston sleeve both rotates and moves axially in the motor cylinder chamber, a seal between the piston and the sidewall of the motor cylinder chamber is subjected to both rotational and axial sliding friction. In addition there are substantial sliding friction losses between the two internal splines and the two external splines.
U.S. Pat. No. 3,961,559 discloses an actuator which includes a piston member which has an internal helical spline and which cooperates with a shaft member on which is fixed an external helical spline. The piston member, when it moves axially on the shaft member, causes rotation of the shaft member due to the cooperation of the helical splines. The piston member itself is restrained from rotating due to the fact that the piston member is located in an oval-shaped cylinder. Fluid pressure applied to opposite sides of the piston will cause the piston to move in one direction or the other and when the piston moves axially relative to the shaft, it will cause rotation of the shaft due to the cooperation of the helical splines between the piston and the shaft. It is necessary in this design not only to provide fluid seals between the outer diameter of the piston and the internal diameter of the cylinder, but also to provide fluid seals between the helical splines of the piston and shaft. Such seals are extremely difficult to manufacture and are not durable and reliable in operation.